The invention relates to a force transmission device, in the following often referred to simply as a device, which is suitable for performing deformation work, comprising a bush having a converging interior, including a particulate filling material in the form of spheres and/or a granulate and a ribbed rod passing through the bush.
In many cases it is desirable for load bearing constructions to possess substantial yieldability whilst retaining their load-bearing capacity. For example, in the context of tunnels, earth moving and mining works, load-bearing constructions are desired which are capable of moving with the deformations of the country rock or earth strata without fracturing. Anchor bolts for example are so designed that the country rock on the excavation side bears against yieldable constructions. The desired yieldability may be attained for example by a connecting member on the tie bolt which slides along the latter under the influence of the rock load, or for example by the provision of a crushing member between the country rock and a fixed point on the tie bolt. Such anchor bolts may be nontensioned or pretensioned.
In the context of tunnelling and mining it has furthermore been proposed to use tubbing constructions of steel or steel-reinforced concrete equipped with crushing zones between the tubbings in order to increase the deformation capacity of the rock support. As the country rock converges into the excavation area, the crushing zones between the tubbings become compressed. Analogously other forms of rock support such as arches, props and the like may be fitted with crushing zone constructions in order to retain their support effect even in the case of country rock deformations.
The aforesaid yielding constructions are employed in mining and tunnelling for protection against chipping off of rock particles and rock pressure bursts. The kinetic energy of the chipping or rock burst action is thus to be converted into deformation energy which by being absorbed in the yielding construction is rendered harmless. The same purpose--the conversion of kinetic energy into deformation energy--is aimed at by yielding means used in transport engineering, e.g. in the form of yielding supports for passengers in vehicles, of crushing zones in vehicles or in the form of catching constructions for vehicles such as for example guide rails, catching nets and buffer blocks having predesigned yielding properties. Similar yielding constructions are employed for protection against avalanches, rock falls and other falling or flying objects.
In order to attain the desired yieldability, anchor heads became known in the context of anchor bolts which by virtue of the country rock pressure slide along a tie bolt. In this case the tie bolt and the anchor head are interengaging bodies, defining a converging space therebetween. The latter accommodates a particulate filling material which is subjected to pressure in the direction of convergence of the intermediate space. Once the tie bolt is moved in relation to the anchor head in the direction of convergence of the intermediate space, the particulate filling material, e.g. spheres, is pressed into the material of the tie bolt or of the anchor head and of the tie bolt. Sliding is thus possible only by the application of force. The described construction comprising an anchor head and a rod acts as a force transmission device in which forces are transmitted preferably in the longitudinal direction of the rod and in which deformation work is done during relative movements between the anchor head and the rod.
The above described force transmission device in the case of anchor bolts as well as other uses of the abovementioned types of yielding constructions is subjected to technical demands depending on the particular application purpose. These demands relate to movement performance under load by the force transmission device, its reliability, its mode of assembly, its corrosion properties, its protection against adverse external effects and the economics of its manufacture.
In order to comply with such particular demands, special designs of the force transmission device are necessary.
For example, it may be required that the transmissible forces of a not pretensioned force transmission device should rise steeply during the initial movements within the device and that major distances of movement, e.g. of 40 cm are attained when large forces are transmitted without fracturing in the force transmission device. Such demands are for example imposed on the force transmission device when it is used for roof bolting where a high degree of yieldability is desired and where the carrying capacity in the initial rock deformation stages should increase steeply.